1. Field of the Invention
This invention relates to an apparatus for multiplexing a specific signal with an amplitude-modulated signal, transmitting and receiving the multiplexed signal, and extracting the specific signal from the multiplexed signal.
2. Description of the Prior Art
In Japan, more than 25 years have passed since the color television broadcasting of the current NTSC (National Television System Committee) system began in 1960. In this period, to answer the requests for a finer definition and higher performance television receiver, various new television systems have been proposed. At the same time, the contents of the programs presented to the viewers have been changed from the mere studio programs or location programs to programs providing images of higher picture quality and higher realistic feeling such as cinema-size movies.
The current broadcasting is specified with 525 scanning lines, 2:1 interlace scanning, a luminance signal horizontal bandwidth of 4.2 MHz, and an aspect ratio of 4:3 (see, for example, Broadcasting Technology Series, Color Television, ed. by Japan Broadcasting Corporation, Japan Broadcasting Corporation Pub., 1961). In this background, several television signal composition methods aiming at compatibility with the current broadcasting system and enhancement of horizontal resolution have been proposed. One of such examples is disclosed in the Japanese Laid-Open Patent No. 59-171387. Considering the NTSC television signal expressed on a two-dimensional plane of temporal frequency f.sub.1 and vertical frequency f.sub.2, chrominance signals C are present in the second and fourth quadrants due to the phase relationship with the chrominance subcarrier fsc. The example uses the vacant first and third quadrants for multiplexing the high frequency components of the luminance signal. The chrominance signal and the multiplexed high frequency components are separated and reproduced at the receiving end, thereby enhancing the horizontal resolution.
In the current television broadcast, as is clear from the description above, the band of signals is limited by the standard, and it is not easy to add some new information in quantity. For example, methods to enhance the horizontal resolution are proposed, but many problems are left unsolved from the viewpoint of the compatibility with the current television broadcasting and the deterioration of demodulation characteristics of high frequency components in a moving picture. Besides, from the standpoint of effective use of the radio wave resources, the transmission band cannot be extended as an easy solution.